1. Field of the Invention
The present invention relates to an adhesive sheet for steel plate and, more particularly, to an adhesive sheet for steel plate which is used to be adhesively bonded to steel plate used in a variety of industrial machines such as transportation machines.
2. Description of the Prior Art
In general, a steel plate for a shell of an automotive vehicle is manufactured in the form of a thin sheet having a thickness generally in the range of 0.6 mm to 0.8 mm, for reduction in weight of a vehicle body. As is known, a steel plate reinforcing sheet is adhesively bonded to the inside of the steel plate for a shell of an automotive vehicle, for the reinforcement purpose.
This steel plate reinforcing sheet is, for example, adhesively bonded in a fabrication process of the steel plate of the shell of the automotive vehicle and thermally foamed by using the heat generated at the time of the electrodeposition coating, to develop its reinforcing property. For example, JP Laid-open (Unexamined) Patent Publication No. Hei 7-68695 proposes a steel plate reinforcing sheet comprising a foaming resin layer and a restricting layer on which the foaming resin layer is laminated.
As the steel plate for the shell of the automotive vehicle is in the form of a thin sheet panel, a fluttering sound is generated from the moving vehicle and an undesired sound or noise is generated from the vehicle door when opened or closed. In order to suppress the generation of the fluttering sound or the undesired sound or noise, JP Laid-open (Unexamined) Patent Publication No. Hei 9-123356 proposes a vibration suppression sheet formed of rubber composition to be laminated on the restricting layer.
Both of the steel plate reinforcing sheet described in JP Laid-open (Unexamined) Patent Publication No. Hei 7-68695 and the vibration suppression sheet described in JP Laid-open (Unexamined) Patent Publication No. Hei 9-123356 use a resin-coated glass fiber cloth, i.e. a glass fiber cloth coated with resin, as the restricting layer. Particularly, the resin-coated glass fiber cloth, which is a glass fiber cloth coated with melamine resin, is used, in terms of heat resistance, workability, and adhesiveness to a foaming resin layer and a damping (vibration suppression) layer.
Meanwhile, from the viewpoint of environmental measures in recent years, strict restrictions are being increasingly required on the emission of organic volatile components from automobile parts and members. The resin-coated glass fiber cloth covered with the melamine resin emits formaldehyde, thus involving the disadvantage that it cannot satisfy such a requirement.
To abate the emission of formaldehyde, epoxy resin is an encouraging alternative. However, when the glass fiber cloth is impregnated with epoxy resin to such an extent that can provide a sufficient seal, the tensile strength and the elasticity of the epoxy-resin-coated glass fiber cloth, serving as the restricting layer, increases excessively. As a result, the workability in punching and cutting processes is reduced and also the fitness in a patterned steel panel is reduced. Thus, this epoxy-resin-coated glass fiber cloth suffers from the disadvantages that sufficient reinforcing effect and vibration suppressing effect cannot be obtained.